1. Field of the Invention
The present invention relates to an image pickup apparatus such as a solid-state image sensor, and more particularly to an image pickup apparatus having a function of suppressing fixed pattern noise.
2. Description of the Related Art
A solid-state image pickup apparatus has its own problems in fixed pattern noise (thereinafter abbreviated to FPN) due to characteristic fluctuations of individual pixels. Various techniques have been proposed so far for canceling the FPN.
For example, a video camera apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-115025 has an FPN suppressing circuit for reading out dark signal in a state free of photoelectric charge, right after resetting the accumulated charge of an image pickup device or while resetting; for A/D converting and accumulating in a storing unit; and for subtracting the dark signal accumulated in the storing unit from the image pickup signals read out from the image pickup device and A/D converted. It further comprises a conversion unit for converting the operation and function of the video camera accompanied by change in dark signal level before the A/D conversion. In cooperation with changeover action of the conversion unit and power supply action, the dark signal is re-entered in the storing unit of the FPN suppressing circuit.
Further, a video camera apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-115026 has an FPN suppressing circuit for reading out dark signal in a state free of photoelectric charge, right after resetting the accumulated charge of an image pickup device or while resetting; for A/D converting and accumulating in a storing unit; and for subtracting the dark signal accumulated in the storing unit from the image signals read out from the image pickup device and A/D converted. In this video camera apparatus, the FPN suppressing circuit is designed to operate by repeating automatically always at predetermined intervals to refresh.